1. Technical Field
The presently disclosed subject matter relates to an LED lighting fixture, and in particular, to an LED lighting fixture for outdoor use that uses LED light sources.
2. Description of the Related Art
Traditionally, lighting fixtures such as incandescent, fluorescent or mercury lighting fixtures are used on roads, parks and other outdoor spaces. These lights are designed to illuminate wide areas and are generally placed high above the ground. The maintenance cost of these lighting fixtures is generally high because they not only use high power incandescent lamps, fluorescent lamps or mercury lamps as their light source, but also require frequent replacement, resulting in additional costs associated with parts and labor.
To decrease the maintenance cost, lighting fixtures using LED light sources have been proposed. As shown in FIG. 1, such a lighting fixture typically includes a plurality of printed boards each arranged to form a part of a “polygon.” Each single printed board includes a plurality of white LEDs mounted on it, all of which has the same directivity.
Each printed board includes a particular number of LEDs each having a particular directivity so that the LEDs can illuminate a desired area at a desired intensity in a specific direction (see, for example, Japanese Patent Application Laid-Open No. 2004-200102).
The lighting fixture described in Japanese Patent Application Laid-Open No. 2004-200102 ensures a wide illumination area in the horizontal direction with respect to the lighting fixture (or the direction along which the printed boards are arranged) since all of the LEDs mounted on the particular printed board point to that direction. However, it can achieve only a narrow illumination area in the direction perpendicular with respect to the lighting fixture (or the vertical direction with respect to the cross section shown in FIG. 1) since all of the LEDs mounted on a particular printed board are directed at the same angle to that direction and, thus, the illumination area in that direction is determined almost solely by the directivity of the LEDs. For this reason, the lighting fixture tends to form an illumination pattern that is biased to one direction and cannot distribute light evenly.